An internal combustion engine and a method for controlling a braking torque of the engine

ABSTRACT

An internal combustion engine includes a cylinder including a piston connected to a rotatable crankshaft, an air guide arranged to guide an air flow to the cylinder an adjustable air flow restriction element arranged to restrict the How through the air guide, an exhaust guide being arranged to guide a gas flow from the cylinder, an adjustable exhaust flow restriction element arranged to restrict the flow through the exhaust guide, an exhaust valve arranged to control a communication between the cylinder and the exhaust guide, and an exhaust valve actuation assembly for actuating the exhaust valve so as to perform in each of a plurality of cycles of the cylinder an exhaust valve actuation sequence, wherein the exhaust valve actuation assembly is adapted to control the commencement of the exhaust valve actuation sequence to occur selectively at any crankshaft angle within a non-zero crankshaft angle interval.

BACKGROUND AND SUMMARY

The invention relates to an internal combustion engine, a vehicle, amethod for controlling an internal combustion engine, a computerprogram, a computer readable medium, and a control unit.

The invention can be applied in heavy-duty vehicles, such as trucks,buses and construction equipment. Although the invention will bedescribed with respect to a heavy-duty vehicle, the invention is notrestricted to this particular vehicle, but may also be used in othervehicles such as a car.

It may be desirable to provide, in particular in heavy-duty vehicles, apowerful engine braking function, e.g. in long downhill road stretcheswith heavy loads. U.S. Pat. No. 5,146,890A describes an engine with athrottling device in the exhaust system so as to increase theback-pressure therein. U.S. Pat. No. 5,146,890A also describes theprovision of exhaust valve opening sequences at the beginning and theend of the compression stroke so as to provide a pressure charge in thecylinder and to avoid a push-back effect at the end of the compressionstroke, respectively.

However, during the engine braking operation, there may be changes inthe circumstances which reduce the braking power, or which entail risksof damaging the engine due to design limits being exceeded. Although thesolution in U.S. Pat. No. 5,146,890A provides an advantageous incrementof the engine braking power, design limits require relatively largemargins for the braking operation which impede maximization of thebraking power.

US2012017369A1 describes a system with a throttle in the exhaust system.The back-pressure causes an intermediate opening of the cylinder outletvalves and a rocker arm mechanism keeps the valve open until the exhaustvalve main opening sequence occurs. This is disadvantageous since theexhaust valves are open during the entire compression stroke, wherebyengine braking power is lost. Also, there is similarly to the solutionin U.S. Pat. No. 5,146,890A a disadvantageous need to consider designlimits which require relatively large margins for the braking operationwhich impede maximization of the braking power.

US20160169127 describes engine braking in an internal combustion enginewith a cylinder outlet valve decompression brake and a brake flap whichis arranged in the exhaust system arranged upstream of a turbochargerexhaust turbine. An engine braking torque is controlled by a level ofclosure of the brake flap. However, a very small change of the brakingflap position may result in a major change of the engine braking torque,making it difficult to achieve during part load engine braking a gooddisability of a vehicle in which the engine is provided.

It is desirable to increase the braking performance of internalcombustion engines in vehicles. It is also desirable to decrease therisks of damage to an engine during a braking operation of the engine.It is also desirable to improve the control of an internal combustionengine braking torque.

According to an aspect of the invention, an internal combustion enginecomprises

a cylinder comprising a piston connected to a rotatable crankshaft,an air guide arranged to guide an air flow to the cylinder,an adjustable air flow restriction clement arranged to restrict the flowthrough the air guide.an exhaust guide being arranged to guide a gas flow from the cylinder,an adjustable flow restriction element arranged to restrict the flowthrough the exhaust guide,an exhaust valve arranged to control a communication between thecylinder and the exhaust guide, andan exhaust valve actuation assembly for actuating the exhaust valve soas to perform in each of a plurality of cycles of the cylinder anexhaust valve actuation sequence,wherein the exhaust valve actuation assembly is adapted to control thecommencement of the exhaust valve actuation sequence to occurselectively at any crankshaft angle within a non-zero crankshaft angleinterval.

By the combination of an adjustable exhaust flow restriction elementarranged to restrict the flow through the exhaust guide, and an exhaustvalve actuation assembly adapted to control the commencement of theexhaust valve actuation sequence to occur selectively at any crankshaftangle within a non-zero crankshaft angle interval, considerableimprovements of the control of engine braking operations are obtained.The exhaust flow restriction element and the exhaust valve actuationassembly may complement each other to provide a close control of theengine braking power. The exhaust flow restriction element may forexample be set for provide an exhaust guide back pressure and a coarsesetting of the engine brake power level, and the exhaust valve actuationassembly may provide a continuous closed loop adjustment to fine tunethe cylinder air mass-flow and the cylinder pressure, to closely adjustthe engine braking power.

More specifically, the exhaust valve actuation assembly being adapted tocontrol the commencement, i.e. an exhaust valve opening event, of theexhaust valve actuation sequence to occur selectively at any crankshaftangle within a non-zero crankshaft angle interval may provide for theexhaust valve actuation assembly providing a continuous adjustment ofthe crankshaft angle of the commencement of the exhaust valve actuationsequence. The exhaust flow restriction element adjustment combined withthe possibility of continuous adjustment of the crankshaft angle of thecommencement of the exhaust valve actuation sequence provides for a highengine braking power capacity combined with a capacity of closelyadjusting the mass flow and the cylinder pressure, e.g. in view of achanging engine speed, which is not provided in prior art solutions. Theexhaust flow restriction element may in itself provide for a highbraking power in a narrow range of engine speeds. The possibility toadjust the commencement of the exhaust valve actuation sequence providesfor retaining a high braking power throughout a wide range of enginespeeds. I.e. with the combination of the exhaust flow restrictionelement and the continuously adjustable exhaust valve actuation assemblyit is possible to obtain a high braking power throughout a wide range ofengine speeds.

The exhaust flow restriction element adjustment combined with thepossibility of continuous adjustment of the crankshaft angle of thecommencement of the exhaust valve actuation sequence also provides forprecisely adjusting the mass flow and the cylinder pressure in responseto changing circumstances during the braking operation, so as to reduceor avoid risks of engine design limits being exceeded. Such limits mayconcern e.g. the cylinder pressure, the turbo rotational speed, or thetemperature in the exhaust manifold. Thereby, the risk of damages ofbreakdown of the engine is reduced.

Also, the improved engine braking operation control and damage avoidancecapacity allows an operation which is closer the design limits of theengine. This in turn allows a further increase in the braking power. Theimproved engine braking control will also provide a smoother, morecomfortable and safer engine braking behaviour of a vehicle providedwith the engine.

In addition, the adjustable air flow restriction element allows for acontrol of partial braking torques with a high precision. This allows agood driveability of a vehicle in which the engine is provided. The airguide presents a lower temperature and less pressure fluctuations thanthe exhaust guide. Also, differing from the exhaust flow restriction,the air flow restriction does not affect the cylinder pressure to anysubstantial degree. As a result, compared to controlling the exhaustflow, controlling the flow restriction in the air guide will result in areduced risk of an overreaction of the braking torque to relativelysmall flow changes.

In summary, the invention provides an improved control of the enginebraking operation in view of changing circumstances during theoperation. This improved control may provide a high braking power overan increased range of engine parameters, in particular engine speed.Also, the invention provides for adjusting the engine braking operationin order to reduce risks of exceeding engine design limits which entailrisks of engine damage. In addition, the invention allows for adjustingthe engine braking torque with a high degree of precision.

Preferably, the exhaust flow restriction element, the exhaust valve andthe exhaust valve actuation assembly are adapted to provide abackpressure for the engine to provide a braking torque, and the airflow restriction element is adapted to enable controllability of saidbraking torque. Thereby, the exhaust flow restriction element, theexhaust valve and the exhaust valve actuation assembly may allow a highmaximum braking torque at a wide engine speed interval, while the airflow restriction element allows a high degree of control of the brakingtorque at a partial load operation.

Preferably, where the engine comprises a turbocharger comprising acompressor, the air guide being arranged to guide the air flow from thecompressor to the cylinder, the adjustable air flow restriction elementis arranged between the compressor and the cylinder. Thereby, the airflow restriction element may operate in a pressure increased by thecompressor, allowing a high degree of responsiveness to air flowrestriction element adjustments. However, in some embodiments, where theair guide is arranged to guide the air flow to the compressor, theadjustable air flow restriction element may be arranged upstream of thecompressor.

Preferably, the air flow restriction clement is arranged to provide aplurality of levels of the air flow restriction depending on theadjustment of the air flow restriction element. The air flow restrictionelement may be adapted to provide the restriction of the air flowrestriction element at any level within a non-zero restriction interval.The air flow restriction element may comprise a throttle valve in theair guide. Thereby, a continuous adjustment of the air flow restrictionmay be provided, which provides for a particularly high level of controlover the engine braking torque.

The engine may have one or more cylinders. It is understood that in someembodiments of a multi cylinder engine, a single air guide may bearranged to guide air to all cylinders of the engine, wherein a singleair flow restriction element is provided to adjustably provide arestriction of the air flow. However, in some embodiments, the cylinder,the air guide and the air flow restriction element may be a firstcylinder, a first air guide and a first air flow restriction element,and the engine may further comprise a second cylinder, a second airguide being arranged to guide an air flow to the second cylinder, and asecond adjustable air flow restriction clement arranged in the secondsir guide to restrict the flow to the second cylinder, wherein the flowto the second cylinder is kept separate from the How to the firstcylinder. Thereby, the engine is provided with two air guides, eachguiding an air flow to a respective cylinder, or a respective sub-groupof cylinders, and each being provided with a respective air flowrestriction element.

The crankshaft angle interval, within which the commencement of theexhaust valve actuation sequence may occur selectively at any crankshaftangle, may be such that it is suitable for providing the increasedcontrol of the engine braking operation discussed above. For example,said interval may extend over 30-50 crankshaft angle degrees, e.g. 40crankshaft angle degrees.

Preferably, the exhaust valve actuation assembly comprises a rotatablecamshaft arrangement, the camshaft arrangement being adapted to providethe control of the commencement of the exhaust valve actuation sequenceto occur selectively at any crankshaft angle within the non-zerocrankshaft angle interval. Where the exhaust valve actuation assemblyincludes a rotatable camshaft, the exhaust valve actuation assembly maybe controllable for adjusting the phase of the camshaft rotation inrelation of the crankshaft rotation. The exhaust valve actuationassembly may comprise a variator for variable valve timing.

Thereby, a robust arrangement is provided for the control tocontinuously vary the crankshaft angle of the commencement of theexhaust valve actuation sequence, i.e. to continuously vary thecrankshaft angle of an exhaust valve opening event of the exhaust valveactuation sequence. Such a cam phasing variable valve actuationmechanism may provide a reliable embodiment which is simple toimplement.

An alternative to cam phasing may be the use of two coaxial camshaftswith a respective cam lobe profile which provide a combined cam lobeprofile with an adjustable length. Thereby one follower may span thepair of closely spaced cam lobes. By changing the duration of the valvelift by advancing one of the cam lobes in the camshaft rotationdirection, an advancement of the commencement of the exhaust valveactuation sequence will also be obtained, and vice versa.

The invention is well-suited for a four-stroke internal combustionengine. The exhaust valve actuation sequence may be a decompressionopening sequence of the exhaust valve commenced in a compression strokeof the respective cycle of the cylinder, the exhaust valve actuationassembly being controllable for selectively providing the decompressionopening sequence. For this, the exhaust valve actuation assembly maycomprise a camshaft presenting at least one cam lobe presenting adecompression nose for the decompression opening sequence, the exhaustvalve actuation assembly being controllable for selectively actuatingthe exhaust valve by means of the decompression nose. Preferably, thedecompression opening sequence of the exhaust valve is commenced in alater half of the compression stroke. Thereby, the decompression openingsequence serves to avoid a push-back effect, which the compressed airwould otherwise have produced at the end of the compression stroke. Inaddition, the possibility of continuous adjustment of the crankshaftangle of the commencement of the decompression opening sequence providesfor a particularly precise and responsive adjustment of the mass flowand the cylinder pressure in response to changing circumstances duringthe braking operation, which effectively serves to provide a highbraking power over a wide engine speed range, and to reduce or avoidrisks of engine design limits being exceeded.

The exhaust valve actuation sequence may be a charging opening sequenceof the exhaust valve commenced in a second half of an intake stroke or afirst half of a compression stroke of the cylinder, the exhaust valveactuation assembly being controllable for selectively providing thecharging opening sequence. For this, the exhaust valve actuationassembly may comprise a camshaft presenting at least one cam lobepresenting a charging nose for the charging opening sequence, theexhaust valve actuation assembly being controllable for selectivelyactuating the exhaust valve by means of the charging nose. Thereby, whenthe piston is at its bottom dead centre, and the compression stroke isabout to start, the exhaust valve opens for a short time period and therelatively higher pressure in the exhaust guide “charges” the cylinder.As a result of this, the braking effect on the piston during thecompression stroke will be considerably higher than without the chargeopening sequence. In addition, the possibility of continuous adjustmentof the crankshaft angle of the commencement of the charge openingsequence provides for a precise and quick adjustment of the mass flowand the cylinder pressure in response to changing circumstances duringthe braking operation, which effectively serves to provide a highbraking power over a wide engine speed range, and to reduce or avoidrisks of engine design limits being exceeded.

Preferably the exhaust flow restriction element is arranged to provide aplurality of levels of the exhaust flow restriction depending on theadjustment of the exhaust flow restriction element. Preferably, theexhaust How restriction element is adapted to provide the restriction ofthe exhaust flow restriction element at any level within a non-zerorestriction interval. Thereby, a continuous adjustment of the exhaustflow restriction may be provided, which in combination with thecontinuous adjustment of the exhaust valve actuation provides for aparticularly high level of control over the engine braking process.

The exhaust flow restriction element may comprise a throttle valve inthe exhaust guide. In some embodiments, an exhaust flow restrictionactuation assembly is provided to adjust the exhaust flow restrictionelement, the exhaust flow restriction element being arranged to assume,upon a fault in the exhaust flow restriction actuation assembly, aposition in which the exhaust flow restriction element does not restrictor block the flow from the cylinder to the turbine. For this, theexhaust flow restriction element may be a throttle valve in the form ofa butterfly valve with a non-symmetric flap. Thereby, in case of a faultin the exhaust flow restriction actuation assembly, the exhaust guidewill be unrestricted and will not impede a later operation in which theengine propels lite vehicle. Thereby a blockage of the exhaust guide incase of a throttle valve malfunction may be avoided, which blockage maymake it impossible to continue driving the vehicle, or even lead to anengine breakdown.

The engine may comprise a turbocharger. The turbocharger may comprise aturbine for extracting power from exhaust gases from the cylinder todrive a compressor for charging air to be guided to the cylinder. Theexhaust guide is thus arranged to guide the gas flow from the cylinderto the turbine, and the adjustable exhaust flow restriction element ispreferably arranged between the cylinder and the turbine. Thus, theexhaust flow restriction element is preferably located upstream of theturbine to restrict the flow from the cylinder to the turbine. Comparedto locating the exhaust flow restriction element downstream of theturbine, the upstream location will increase the turbo speed and airmass flow through the engine, whereby the engine braking power may beincreased with 50%. The upstream exhaust flow restriction elementcreates a high back pressure in the exhaust manifold without reducingturbo performance. The upstream location of the exhaust flow restrictionelement allows the turbocharger to be effective within a larger enginespeed range, which in turn increases the available engine speed rangecontrollable by the exhaust valve actuation assembly and the exhaustflow restriction element. Thereby the control provided by thecombination of the exhaust valve actuation assembly and the exhaust flowrestriction element is further enhanced. Thus, continuous adjustmentprovided by the exhaust valve actuation assembly and the location of theexhaust flow restriction element between the cylinder and the turbineprovides a particularly high engine braking power throughout a largeengine speed range. As a result of providing the increase of the turbospeed and the air mass flow, the upstream location of the exhaust flowrestriction element will also decrease the exhaust temperature at theturbine.

The cylinder, the exhaust guide and the exhaust flow restriction elementmay be a first cylinder, a first exhaust guide and a first exhaust flowrestriction element, and the engine may further comprise a secondcylinder, a second exhaust guide being arranged to guide a gas flow fromthe second cylinder to the turbine, and a second adjustable exhaust flowrestriction element arranged upstream of the turbine to restrict theflow from the second cylinder to the turbine, wherein the flow from thesecond cylinder to the turbine is kept separate from the flow from thefirst cylinder to the turbine. Thereby, the engine is provided with twoexhaust guides, each guiding a gas flow from a respective cylinder, or arespective sub-group of cylinders, and each being provided with arespective exhaust flow restriction element. This makes it possible toseparate in an advantageous manner the exhaust pulses from the cylindersall the way to the turbine. More specifically, it is possible to matchthe exhaust guides to the cylinders so that the exhaust pulses do notsuppress each other before reaching the turbine. In turn this providesfor increasing the power of the turbine, in turn increasing the turbocharging pressure and the air mass flow, which increases the enginebraking power. Thus, the performance during engine braking of the enginewill be improved.

It is understood however that in some embodiments of a multi cylinderengine, a single exhaust guide may be arranged to guide a gas flow fromalt cylinders of the engine to a turbine of a turbocharger, wherein asingle exhaust flow restriction element is provided to adjustablyprovide a restriction of the gas flow.

The turbocharger may be a fixed geometry turbocharger with a turbine inone, two or more steps. In some embodiments, the engine comprises avariable geometry turbocharger comprising a turbine, the exhaust guidebeing arranged to guide the gas flow from the cylinder to the turbine,wherein the turbocharger is arranged to provide at the turbine anadjustable restriction of the gas flow in addition to the restrictionwhich the adjustable exhaust flow restriction element is arranged toprovide. Thereby, as exemplified below, a further improvement of thecontrol of the engine braking operation may be provided, with a controlof the air mass flow and the cylinder pressure by means of the exhaustvalve actuation assembly, the air flow restriction element, the exhaustflow restriction element as well as the variable geometry turbocharger.

In some embodiments, where the engine comprises a variable geometryturbocharger comprising a turbine, the exhaust guide being arranged toguide the gas flow from the cylinder to the turbine, the adjustableexhaust flow restriction element may be provided by a flow adjustingfunction at the turbine. Thereby, the exhaust flow restriction elementmay be integrated with the variable geometry turbocharger, which reducesthe complexity of the engine.

According to another aspect of the invention, a method is provided ofcontrolling an internal combustion engine in a vehicle comprising acylinder, a fuel system for supplying fuel to the cylinder, an air guidearranged to guide an air flow to the cylinder, an exhaust guide arrangedto guide a gas flow from the cylinder, an exhaust valve arranged tocontrol a communication between the cylinder and the exhaust guide, themethod comprising

controlling the engine to provide a braking torque, the controlcomprising,terminating the supply of fuel to the cylinder,restricting the flow through the exhaust guide,restricting the flow through the air guide, andperforming in each of a plurality of cycles of the cylinder an exhaustvalve actuation sequence,the control of the engine to provide a braking torque also comprisingdetermining a value of an engine parameter affecting the pressure in thecylinder and/or the air mass flow through the cylinder,in dependence on the determined engine parameter value adjusting thetiming of a commencement of the exhaust valve actuation sequence, andin dependence on at least one of the at least one determined engineparameter value adjusting the restriction of the flow through the airguide.

The method may be advantageously performed in a four stroke internalcombustion engine. It is understood that the method may include controlof the engine braking torque to a drivetrain of the vehicle. The enginemay comprise a turbo changer comprising a turbine, the exhaust guidebeing arranged to guide the gas flow from the cylinder to the turbine.It is understood that restricting the flow through the exhaust guide maycomprise adjusting an adjustable exhaust flow restriction elementarranged to restrict the flow through the exhaust guide. It is alsounderstood that restricting the flow-through the air guide may compriseadjusting an adjustable air flow restriction element arranged torestrict the flow through the air guide.

Similarly to the engine described above, the combination of therestriction of the flow through the exhaust guide, and the adjustment ofthe timing of the commencement of the exhaust valve actuation sequencein dependence on the determined value of the engine parameter affectingthe pressure in the cylinder and/or the air mass flow through thecylinder, provides for retaining a high braking power throughout a widerange of engine speeds. Also, said combination provides for reducing oravoiding risks of engine design limits being exceeded. Also similarly tothe engine described above, the adjustable air flow restriction elementallows for a control of partial braking torques with a high precision.Controlling the flow restriction in the air guide will result in areduced risk of an overreaction of the braking torque to relativelysmall flow changes.

Preferably, adjusting the timing of the commencement of the exhaustvalve actuation sequence comprises adjusting the crankshaft angle atwhich the exhaust valve actuation sequence is commenced. Preferably,apart from the crankshaft angle at which the exhaust valve actuationsequence is commenced, the exhaust valve actuation sequence during oneof the cycles is identical to the exhaust valve actuation sequenceduring another of the cycles. Such an adjustment may be advantageouslyprovided by a camshaft phasing solution described above.

Preferably, each of the at least one the engine parameter is one of theengine rotational speed, a requested engine braking torque, a currentengine braking torque, a pressure in the air guide, a rotational speedof a turbocharger of the engine, and a pressure in the exhaust guide. Byusing any of these parameters for adjusting the timing of thecommencement of the exhaust valve actuation sequence and for adjustingthe restriction of the flow through the air guide, an effective controlof the air mass flow and the cylinder pressure may be provided. Forexample, the exhaust valve actuation sequence may be performed during afirst cycle of the cylinder at a first rotational speed of the engine,and the exhaust valve actuation sequence may also be performed during asecond cycle of the cylinder at a second rotational speed of the engine,the second rotational speed being higher than the first rotationalspeed, the exhaust valve actuation sequence being performed at a lowercrankshaft angle in the second cycle than in the first cycle. Thereby,the mass flow and cylinder pressure may be effectively controlleddespite a varying engine speed.

Preferably, adjusting the restriction of the flow through the air guidecomprises adjusting a throttle valve in the air guide. Thereby a simpleand effective way of obtaining a high precision partial engine braketorque may be provided.

Preferably, the adjustment of the restriction of the flow through theair guide is a closed loop adjustment. The feedback parameter for such aclosed loop control may be any suitable parameter, such as the air guidepressure or the air guide mass flow. Thus, a pressure in the air guidemay be a feedback parameter in the closed loop adjustment. Where acompressor is provided in the air guide, preferably the boost pressurein the air guide is a feedback parameter. In some embodiments, apressure in the exhaust guide, preferably upstream of the restriction ofthe flow through the exhaust guide, is a feedback parameter in theclosed loop adjustment. In some embodiments, a pressure differenceacross the cylinder is a feedback parameter in the closed loopadjustment. Adjusting the timing of the commencement of the exhaustvalve actuation sequence may comprise adjusting the crankshaft angle atwhich the exhaust valve actuation sequence is commenced. The adjustmentof the timing of the commencement of the exhaust valve actuationsequence may be an open loop adjustment. As exemplified below, theexhaust flow restriction and the timing of the commencement of theexhaust valve actuation sequence may be adapted in open loop controlalgorithms to provide a backpressure for the engine to provide a brakingtorque, and the air flow restriction may be adjusted in a closed loop toprovide a high precision control of the braking torque at partial load.

Alternatively, the adjustment of the timing of the commencement of theexhaust valve actuation sequence and/or the adjustment of therestriction of the flow through the exhaust guide may be a closed loopadjustment. Thereby, a pressure in the air guide may be a feedbackparameter in the closed loop adjustment. Where a compressor is providedin the air guide, preferably the boost pressure in the air guide is afeedback parameter. In some embodiments, a pressure in the exhaustguide, preferably upstream of the restriction of the flow through theexhaust guide, is a feedback parameter in the closed loop adjustment. Insome embodiments, a pressure difference across the cylinder is afeedback parameter in the closed loop adjustment.

Preferably, the method comprises determining a value of a further engineparameter affecting the pressure in the cylinder and/or the air massflow through the cylinder, and in dependence on the determined furtherengine parameter value adjusting the restriction of the How through theexhaust guide. The further engine parameter may be the engine rotationalspeed, the engine torque, a pressure in an air guide arranged to guidean air flow from a compressor of a turbocharger of the engine to diecylinder, a rotational speed of the turbocharger. or a pressure in theexhaust guide. Thereby, the exhaust flow restriction, the air flowrestriction as well as the timing of the commencement of the exhaustvalve actuation sequence may be effectively controlled based onparameters affecting the pressure in the cylinder and/or the air massflow through the cylinder. This will provide a particularly high levelof control of the engine braking operation. As exemplified below, one ortwo of the exhaust flow restriction, the air flow restriction and thetiming of the commencement of the exhaust valve actuation sequence maybe subjected to an open loop control while the remaining of the exhaustflow restriction, the air flow restriction and the timing of thecommencement of the exhaust valve actuation sequence may beadvantageously subjected to a closed loop control. It is alsoconceivable within the scope of an aspect of the invention to arrangeall of the exhaust flow restriction, the air flow restriction and thetiming of the commencement of the exhaust valve actuation sequence to besubjected to an open loop control. It is further conceivable within thescope of an aspect of the invention to arrange all of the exhaust flowrestriction, the air flow restriction and the timing of the commencementof the exhaust valve actuation sequence to be subjected to a closed loopcontrol.

As understood from the description of the engine above, restricting theflow through the exhaust guide may comprise adjusting a throttle valvein the exhaust guide, and/or adjusting a flow adjustment function at aturbine of a variable geometry turbocharger of the engine, wherein theexhaust guide is arranged to guide the gas flow from the cylinder to theturbine.

The exhaust valve actuation sequence may comprise a decompressionopening sequence commenced in a compression stroke of the cylinder. Theexhaust valve actuation sequence may also comprise a charging openingsequence of the exhaust valve commenced in a second half of an intakestroke or a first half of a compression stroke of the cylinder.Preferably the method comprises reducing the degree of opening of theexhaust valve between the charging opening sequence and thedecompression opening sequence. Preferably the method comprises fullyclosing the exhaust valve between the charging opening sequence and thedecompression opening sequence. Thereby the braking power may beincreased or maximized at the compression stroke, since a reduced or nocommunication is provided between the cylinder and the exhaust guide,allowing a very high pressure to build up in the cylinder.

It is understood that that the exhaust valve actuation sequence maycomprise a main opening sequence of the exhaust valve with a maximumdegree of opening of the exhaust valve in an exhaust stroke of thecylinder.

As suggested above, the method may comprise, in dependence on at leastone of the at least one determined engine parameter value, adjusting therestriction of the flow through the exhaust guide. The adjustment of therestriction of the flow through the exhaust guide is advantageously donein an open loop adjustment. Restricting the flow through the exhaustguide may comprise adjusting a throttle valve in the exhaust guide, andor adjusting a flow adjustment function at a turbine of a variablegeometry turbocharger of the engine, wherein the exhaust guide isarranged to guide the gas flow from the cylinder to the turbine.

According to another aspect of the invention, an internal combustionengine comprises a cylinder comprising a piston connected to a rotatablecrankshaft,

an air guide arranged to guide an air flow to the cylinder,an adjustable air flow restriction element arranged to restrict the flowthrough the air guide,an exhaust guide being arranged to guide a gas flow from the cylinder,an exhaust valve arranged to control a communication between thecylinder and the exhaust guide, andan exhaust valve actuation assembly for actuating the exhaust valve soas to perform in each of a plurality of cycles of the cylinder anexhaust valve actuation sequence,wherein the exhaust valve actuation assembly is adapted to control thecommencement of the exhaust valve actuation sequence to occurselectively at any crankshaft angle within a non-zero crankshaft angleinterval.

The adjustment of the timing of a commencement of the exhaust valveactuation sequence may provide a high engine brake power, and anadjustment of the air flow restriction element may provide a high degreeof control of the engine brake power at partial load. Preferably, wherethe engine comprises a turbocharger comprising a compressor, the airguide being arranged to guide the air flow from the compressor to thecylinder, the adjustable air flow restriction element is arrangedbetween the compressor and the cylinder. Alternatively, the adjustableair flow restriction element may be arranged upstream of the compressor.Preferably, the air flow restriction element is arranged to provide aplurality of levels of the air flow restriction depending on theadjustment of the air flow restriction element. Preferably, the air flowrestriction element is adapted to provide the restriction of the airflow restriction element at any level within a non-zero restrictioninterval. The air flow restriction element may comprise a throttle valvein the air guide. The exhaust valve actuation assembly may include arotatable camshaft, wherein the exhaust valve actuation assembly iscontrollable for adjusting the phase of the camshaft rotation inrelation of the crankshaft rotation. The exhaust valve actuationsequence may be a decompression opening sequence of the exhaust valvecommenced in a compression stroke of the respective cycle of thecylinder, the exhaust valve actuation assembly being controllable forselectively providing the decompression opening sequence. The exhaustvalve actuation sequence may be a charging opening sequence of theexhaust valve commenced in a second half of an intake stroke or a firsthalf of a compression stroke of the cylinder, the exhaust valveactuation assembly being controllable for selectively providing thecharging opening sequence.

According to another aspect of the invention, a method is provided ofcontrolling an internal combustion engine in a vehicle comprising acylinder, a fuel system for supplying fuel to the cylinder, an air guidearranged to guide an air flow to the cylinder, an exhaust guide arrangedto guide a gas flow from the cylinder, an exhaust valve arranged tocontrol a communication between the cylinder and the exhaust guide, themethod comprising

controlling the engine to provide a braking torque, the controlcomprising,terminating the supply of fuel to the cylinder,restricting the flow through the air guide, andperforming in each of a plurality of cycles of the cylinder an exhaustvalve actuation sequence, the control of the engine to provide a brakingtorque also comprisingdetermining a value of at least one engine parameter affecting thepressure in the cylinder and/or the air mass flow through the cylinder.in dependence on at least one of the at least one determined engineparameter value adjusting the timing of a commencement of the exhaustvalve actuation sequence, andin dependence on at least one of the at least one determined engineparameter value adjusting the restriction of the flow through the airguide.

The adjustment of the timing of a commencement of the exhaust valveactuation sequence may provide a high engine brake power, and theadjustment of the restriction of the flow through the air guide mayprovide a high degree of control of the engine brake power at partialload. The at least one the engine parameter may be one of the enginerotational speed, a requested engine braking torque, a current enginebraking torque, a pressure in the air guide, a rotational speed of aturbocharger of the engine, and a pressure in the exhaust guide.Adjusting the restriction of the flow through the air guide may compriseadjusting a throttle valve in the air guide. Preferably, the adjustmentof the restriction of the flow through the air guide is a closed loopadjustment. Preferably, adjusting the timing of the commencement of theexhaust valve actuation sequence comprises adjusting the crankshaftangle at which the exhaust valve actuation sequence is commenced.Preferably, the adjustment of the timing of the commencement of theexhaust valve actuation sequence is an open loop adjustment. The exhaustvalve actuation sequence may comprise a decompression opening sequencecommenced in a compression stroke of the cylinder. The exhaust valveactuation sequence may comprise a charging opening sequence of theexhaust valve commenced in a second half of an intake stroke or a firsthalf of a compression stroke of the cylinder.

Further advantages and advantageous features of the invention aredisclosed in the following description and in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

With reference to the appended drawings, below follows a more detaileddescription of embodiments of the invention cited as examples.

In the drawings:

FIG. 1 is a side view of a vehicle in the form of a truck.

FIG. 2 is a schematic drawing of an internal combustion engine in thevehicle in FIG. 1.

FIG. 3 is a view of a vertical cross-section at a cylinder of the enginein FIG. 2.

FIG. 4 is a diagram of actuation sequences of exhaust valves shown inFIG. 3 as functions of the crankshaft angle.

FIG. 5 is a block diagram depicting steps in a method of controlling theengine in FIG. 2.

FIG. 6-FIG. 9 are block diagrams depicting steps in methods ofcontrolling an engine according to alternative embodiments of theinvention.

FIG. 10 shows an exhaust flow restriction element for an engineaccording to an additional embodiment of the invention.

FIG. 11 is a view of a vertical cross-section at a cylinder of an engineaccording to a further embodiment of the invention.

FIG. 12 is a block diagram depicting steps in a method of controllingthe engine in FIG. 11.

DETAILED DESCRIPTION

FIG. 1 shows a vehicle in the form of a truck, or a tractor for asemitrailer. It should be noted that the vehicle can be of a variety ofalternative types, e.g. it maybe a car, a bus, or a working machine suchas a wheel loader. The vehicle comprises a four-stroke internalcombustion engine 1.

As can be seen in FIG. 2, the engine in this example comprises sixcylinders 301, 302 arranged in a line. The engine 1 is oriented in thevehicle such that line of cylinders is parallel with the direction ofstraight travel of the vehicle. It should be noted however that inalternative embodiments the orientation of the engine may have anotherorientation in the vehicle. For example it may be a transverse engine,i.e. an engine installed such that the crankshaft of the engine isperpendicular to the direction of straight travel of the vehicle. Thismaybe the case e.g. in a bus, where the engine may be a transverseengine mounted in the rear of the bus, The cylinders include firstcylinders 301 which are the three cylinders located forward in thevehicle direction of forward travel, and second cylinders 302 which arethe three cylinders located rearward in the vehicle direction of forwardtravel.

The engine comprises a turbocharger 4 comprising a turbine 401 in anexhaust conduit arrangement 501, 502 of die engine. The turbocharger 4also comprises a compressor 402 in an air guide 901 arranged to guide anair flow from the compressor 402 to the cylinders 301, 302 via a chargeair cooler 902. The turbine 401 and the compressor 402 are fixedlyconnected and rotatable. whereby the turbine 401 is arranged to liedriven by gases in the exhaust conduit arrangement 501, 502, to drivethe compressor 402 which is arranged to compress air in the air guide901, as in known per se.

The exhaust conduit arrangement comprises a first exhaust guide 501arranged to guide a gas flow from the first cylinders 301 to the turbine401, and a second exhaust guide 502 arranged to guide a gas flow fromthe second cylinders 302 to the turbine 401. Thereby, the flow from thesecond cylinders 302 to the turbine 401 is kept separate from the flowfrom the first cylinders 301 to the turbine.

A control unit 21 is arranged to determine values of engine parametersaffecting the pressure in the cylinders and/or the air mass flow throughthe cylinders 301, 302. These parameters include a requested enginetorque determined based on a requested vehicle speed provided from avehicle speed control function, an actual vehicle speed, and theselected gear ratio of a transmission in the vehicle. The parametersalso includes the engine rotational speed, which is determined by meansof an engine speed sensor as described below. The engine parametersaffecting the pressure in the cylinders and/or the air mass flow furtherincludes the pressure in the air guide 901, determined by means ofsignals from an air guide pressure sensor 211. Also, the control unit 21is arranged to determine the pressure in the exhaust guides 501, 502based on signals from an exhaust guide pressure sensor 214 in the firstexhaust guide 501. Alternatively, an additional exhaust guide pressuresensor may be provided in the second exhaust guide 502, or an exhaustguide pressure sensor may be provided in the second exhaust guide 502only. Further, the control unit 21 is arranged to access a data storageunit 213 provided with data correlating values of the engine torque andthe engine rotational speed with desired values of the air guidepressure.

An adjustable air flow restriction element, comprising a throttle valve903 in the air guide 901, is arranged to restrict the flow through theair guide 901. The adjustable air flow restriction element 903 isarranged between the compressor 402 and the cylinders 301,302, morespecifically, between the charge air cooler 902 and the cylinders 301,302. The air guide pressure sensor 211 is located between the adjustableair flow restriction clement 903 and the cylinders 301, 302. Inalternative embodiments, the adjustable air flow restriction element 903may be arranged upstream of the compressor 402.

The air flow restriction element 903 is controllable by the control unit21 via an air flow restriction actuation assembly (not shown) comprisinge.g. a stepper motor. In addition, a position sensor (not shown) at theair flow restriction element 903 is connected to the control unit 21,and arranged to register and send to the control unit signalsrepresentative of the position of the air restriction element 903, for aposition feedback. It should be noted that any alternative type of airflow restriction actuation assembly may be provided; for example such asassembly may include a brushless motor or a pneumatic motor. The airflow restriction element 903 is adapted to provide the air restrictionat any level within a non-zero restriction interval depending on theadjustment of the air flow restriction element 903.

A first adjustable exhaust flow restriction element 601 in the form of afirst exhaust throttle valve is arranged in the first exhaust guide 501,between the first cylinders 301 and the turbine 401. The exhaust guidepressure sensor 214 is located between the first adjustable exhaust flowrestriction element 601 and the cylinders 301. A second adjustableexhaust flow restriction element 602 in the form of a second exhaustthrottle valve is arranged in the second exhaust guide 502, between thesecond cylinders 302 and the turbine 401. The first and second exhaustflow restriction elements are provided as “draw bridge” valves, whichmay be arranged to not provide any obstacle to the flow when fully open.Each valve 601, 602 may be provided in a unit which is bolted onto therespective exhaust guide 501, 502. It should be noted however, that inalternative embodiments, each valve may be integrated into therespective exhaust guide. In a further alternative, a valve may beintegrated in housing of the turbine. As also mentioned elsewhereherein, a restriction element may be provided by the flow adjustmentfunction of a variable geometry turbocharger. Each of the first andsecond exhaust flow restriction elements 601, 602 are controllable bythe control unit 21 via a respective exhaust flow restriction actuationassembly (not shown) comprising e.g. a stepper motor. In addition, aposition sensor (not shown) at each exhaust flow restriction element601, 602 is connected to the control unit 21, and arranged to registerand send to the control unit signals representative of the position ofthe respective exhaust flow restriction element 601, 602, for a positionfeedback. It should be noted that any alternative type of exhaust flowrestriction actuation assembly may be provided; for example such asassembly may include a brushless motor or a pneumatic motor.

Each of the first and second exhaust flow restriction elements 601, 602is arranged to provide a plurality of levels of the exhaust flowrestriction depending on the adjustment by the control unit 21 of therespective exhaust flow restriction element 601, 602. More specificallyeach exhaust flow restriction element 601, 602 is arranged to provide acontinuous adjustment of the flow, i.e. to provide a flow restriction atany level within a non-zero restriction interval. The data storage unit213 is provided with data correlating values of the engine torque andthe engine rotational speed with settings for the first and secondexhaust flow restriction elements 601, 602.

It should be noted that in alternative embodiments, a single exhaustguide may be arranged to guide exhaust gases from all cylinders of theengine. In some embodiments, a single exhaust flow restriction element601 may be provided downstream of the turbine of the turbocharger. Infurther embodiments, the turbocharger 4 may be a variable geometryturbocharger, whereby the turbocharger 4 provides, with a flow adjustingfunction at the turbine 401, the function of the exhaust flowrestriction element 601 as described herein.

At each of the cylinders 301, 302 two intake valves (not shown) areprovided to control the admission of air from the air guide 901 to therespective cylinder 301, 302. Also, at each of the cylinders two exhaustvalves, described closer below, are arranged to control a communicationbetween the respective cylinder 301, 302 and the respective exhaustguide 501, 502. It should be noted that in other embodiments only one ormore than two exhaust valves may be provided at each cylinder.

Also, a fuel system (not shown) is provided to inject fuel into thecylinders during cycles thereof, and the fuel injection is controllableby the control unit 21.

The engine 1 comprises an exhaust valve actuation assembly 8 comprisinga camshaft arrangement comprising a rotatable camshaft 801. At eachcylinder 301, 302 a cam lobe 803 is fixed to the camshaft for actuationof the exhaust valves as described closer below. The exhaust valveactuation assembly 8 also comprises a variator 802 for variable valvetiming, more particularly for adjustment of the phase of the camshaftrotation, as described closer below.

Reference is made also to FIG. 3 showing a cross-section through one ofthe first cylinders 301. Each cylinder 301, 302 comprises a piston 303connected to a rotatable crankshaft 101. The control unit 21 is arrangedlo determine the engine speed by means of signals from an engine speedsensor 212 at the crankshaft 101. In alternative embodiments, a sensormay be arranged to detect the speed of the camshaft 801, whereby thecrankshaft speed may be obtained by doubling the sensed camshaft speed.FIG. 3 also shows one of the exhaust valves 7 arranged to control thecommunication between the first cylinder 301 and the first exhaust guide501. FIG. 3 further shows the first adjustable exhaust flow restrictionelement 601 in the first exhaust guide 501. In addition, one of theintake valves 11, arranged to control the communication between thefirst cylinder 301 and the air guide 901, is shown. For actuation ofintake valves the engine 1 comprises an intake valve actuation assembly12 which may comprise a camshaft arrangement with a rotatable camshaft(not show). FIG. 3 also shows the adjustable air flow restrictionelement 903 in the air guide 901.

The exhaust valve actuation assembly S comprises for each cylinder 301,302 a rocker arm 807 arranged to pivot by contact at one end with therespective cam lobe 803 to actuate the exhaust valves 7. The cam lobe803 presents a relatively large main nose 804, and two relatively smallnoses, i.e. a decompression nose 805 and a charge nose 806.

When the engine propels the vehicle, a distance is provided between onone hand the rocker arm 807 and on the other hand the decompression nose805 and the charge nose 806. Therefore decompression nose 805 and thecharge nose 806 do not provide any exhaust valve actuation when theengine propels the vehicle. However, during engine braking, the rockerarm 807 is in contact with the decompression nose 805 and the chargenose 806, which provide exhaust valve actuation sequences as describedbelow.

The selective engagement of the decompression nose 805 and the chargenose 806 is provided by a hydraulic piston 808 at an end of the rockerarm 807 opposite to the end at which the rocker arm 807 is in contactwith the cam lobe 803. The hydraulic piston 808 is controlled by ahydraulic conduit system and a control valve 809 in each rocker arm 807,each control valve 809 being controllable by the control unit 21.

Reference is made also to FIG. 4 showing a diagram of actuationsequences of the exhaust valves shown in FIG. 3 as functions of thecrankshaft angle. At each cylinder 301, 302 the main nose 804 of the thecam lobe 803 is arranged to actuate the exhaust valves 7 so as toperform in each of a plurality of cycles of the respective cylinder301,302 an exhaust valve actuation sequence in the form of a mainopening sequence MOSL. The main opening sequence MOSL. which duringoperations in which the engine propels the vehicle serves to expelexhaust gases from the cylinder, commences in an expansion stroke, andpresents a maximum degree of opening of the exhaust valves 7 in anexhaust stroke of the cylinder 301, 302. When the engine propels thevehicle, the rocker arm avoids contact with the decompression nose 805and the charge nose 806 of the cam lobe as described above.

FIG. 4 also shows an intake valve opening sequence IOS performed by theintake valves at the cylinder.

When engine braking is commenced, the rocker arm is brought into contactwith the decompression nose 805 and the charge nose 806 by control ofthe hydraulic piston 808 of the rocker arm 807 described above. As aresult the lift by the main nose is also increased somewhat so that themain opening sequence appears as indicated by the curve MOS1 in FIG. 4.

In addition, the decompression nose 805 provides a decompression openingsequence DOS1, which is commenced in a compression stroke of thecylinder 301. The decompression opening sequence DOS1 serves to releasethe air compressed during the compression stroke. Thereby, thedecompression opening sequence DOS1 serves to avoid a push-back effect,which the compressed air would otherwise have produced at the end of thecompression stroke.

Further during engine braking, the charge nose 806 provides a chargeopening sequence COS1, which is commenced in a second half of an intakestroke of the cylinder 301. Thereby, when the piston 303 is at itsbottom dead centre and the compression stroke is about to start, theexhaust valves 7 open for a short period and the relatively higherpressure in the exhaust guide 501 “charges” the cylinder. As a result ofthis, the braking effect on the piston 303 during (he compression strokewill be considerably higher than without the charge opening sequenceCOS1. It should be noted that the exhaust valves 7 are fully closedbetween the charging opening sequence COS1 and the decompression openingsequence DOS1. In alternative embodiments the degree of opening of theexhaust valves 7 may be merely reduced, without involving a completeclosure of the exhaust valves, between the charging opening sequenceCOS1 and the decompression opening sequence DOS1.

It should be noted that in alternative embodiments the charge nose 806and the decompression nose 805 may be provided on a separate cam lobeadjacent to a cam lobe provided with the main nose 804. Thereby. therocker arm may be provided in two parts, each following a respective ofthe cam lobes, although only the part following the cam lobe with themain nose is arranged to actuate the exhaust valves by default. Therocker arm parts may be provided with an engagement mechanism forselectively fixing the rocker arm parts to each other when the chargenose 806 and the decompression nose 805 are to provide the correspondingactuation sequences of the exhaust valves 7. In such embodiments, thelift by the main nose 804 may remain unchanged regardless of theengagements of the charge nose 806 and the decompression nose 805.

By means of said variator 802 (FIG. 2) and the possibility to adjust thephase of the camshaft rotation, the commencement of the exhaust valveactuation sequences MOS1, DOS1, COS1 may be controlled to occurselectively at any crankshaft angle within a non-zero crankshaft angleinterval. In fact the entire exhaust valve actuation sequences MOS1,DOS1. COS1 may be moved within the non-zero crankshaft angle interval.Said interval may extend over e.g. 40 crankshaft angle degrees. Otherinterval sizes are of course possible within the scope of an aspect ofthe invention. The data storage unit 213 is provided with datacorrelating values of the engine torque and the engine rotational speedwith settings for the phase of the camshaft rotation.

FIG. 4 shows examples of adjusted crankshaft values obtained by thecamshaft phase adjustments. By moving the camshaft phase in thedirection of rotation of the camshaft 801, the exhaust valve actuationsequences are moved forward in the cycles as indicated by the curvesMOS2, DOS2, COS2 in FIG. 4. By moving the camshaft phase opposite to thedirection of rotation of the camshaft 801, the exhaust valve actuationsequences are moved backwards in the cycles as indicated by the curvesMOS3, DOS3, COS3 in FIG. 4. It should be noted that, apart from thecrankshaft angle at which the respective exhaust valve actuationsequence is commenced, the exhaust valve actuation sequences areidentical in all cycles. For improved control of the engine brakingperformance the camshaft phase adjustments are made in dependence onengine parameters as described below.

With reference to FIG. 5 a method of controlling the engine 1 to providea braking torque will be described.

When the engine braking is commenced, the supply of fuel to thecylinders 301, 302 is terminated S1.

The control valves 809 in the rocker arms 807 at the cylinders 301, 302are controlled to actuate the hydraulic pistons 808 to engage the rockerarms 807 with the decompression noses 805 and the charge noses 806.Thereby the charging opening sequence COS1 and the decompression openingsequence DOS1 are added S2 to the cycles in the cylinders as describedabove.

The method also comprises determining S3 the requested engine torque andthe engine rotational speed. The control unit 21 determines by means ofthe data in the data storage unit 213 a setting for the first and secondexhaust flow restriction elements 601, 602 based on the determinedvalues of the engine torque and the engine rotational speed. The exhaustflow restriction elements 601, 602 are adjusted S4 to the determinedsetting, so as to provide a restriction of the air flows in the exhaustguides 501, 502 correlated with the determined requested engine torqueand engine rotational speed. This adjustment is an open loop adjustment,i.e. although it is updated based on changes in the requested enginetorque and engine rotational speed, it is not updated with feedback fromany parameter from which the air flow through the cylinders or thecylinder pressure may be determined.

The control unit 21 also determines, based on the requested enginetorque and the engine rotational speed, by means of the data in the datastorage unit 213, a setting for the camshaft phase. In an open loopcontrol, the control unit 21 sends signals to the variator 802 so as toadjust S4 the phase of the camshaft rotation to adjust the crankshaftangles of the exhaust valve actuation sequences MOS1, DOS1, COS1.Retarding the commencement of the exhaust valve actuation sequencesMOS1, DOS1, COS1 will reduce the pressure in the air guide 901 whichwill reduce the braking torque, and vice versa.

Based on the determined requested engine torque and engine rotationalspeed, the control unit 21 determines S5 based on the data in thestorage unit 213 a desired air guide pressure value. In a closed loopcontrol, the control unit 21 sends signals to the air flow restrictionelement 903 in the air guide 901 so as to adjust S6 the air flowrestriction element 903, based on the desired air guide pressure valueand feedback signals from the air guide pressure sensor 211. In theclosed loop control, the feedback signals from the air guide pressuresensor 211 are compared S7 to the desired air guide pressure value.Moving the air flow restriction element 903 towards a fully closedposition will reduce the pressure in the air guide 901. and vice versa.It should be noted that instead of using a pressure sensor, the airguide pressure may be determined by the control unit 21 based on someother suitable parameter, such as a measured air mass flow in the airguide 901.

It should be noted that as an alternative to the air guide pressure, theclosed loop air flow restriction element 903 adjustment may be donebased on some other suitable parameter as a feedback parameter, such asthe pressure in the exhaust guide 501, 502, or the rotational speed ofthe turbocharger 4. In the case of the exhaust guide pressure, thefeedback signals may be obtained from exhaust guide pressure sensors atthe exhaust guides 501, 502. In the case of the turbo charger rotationalspeed, the feedback signals may be obtained from a speed sensor at theturbocharger 4. In some embodiments, the pressure in the exhaust guide501, 502, or the rotational speed of the turbocharger 4 may bedetermined by the control unit 21 based on other suitable parameters.For example, the control unit 21 may the arranged to use mathematicalmodels for the pressure in the exhaust guide 501, 502 and the rotationalspeed of the turbocharger 4. E.g. the control unit 21 may be arranged todetermine these parameters based on the engine speed and the enginebraking torque as well as measured values of the air guide pressure andthe air mass flow.

With reference is made to FIG. 6, an alternative embodiment of themethod will be described. Therein steps are identical to the steps inthe embodiment described with reference to FIG. 5, except for thefollowing differences: Based on the determined requested engine torqueand engine rotational speed, the control unit 21 determines S5 based onthe data in the storage unit 213 a desired pressure difference acrossthe cylinders 301, 302. In a closed loop control, the control unit 21sends signals to the air flow restriction element 903 in the air guide901 so as to adjust S6 the air flow restriction element 903, based onthe desired pressure difference across the cylinders 301, 302 andfeedback signals from the air guide pressure sensor 211 and the exhaustguide pressure sensor 214. In the closed loop control, the feedbacksignals from the air guide pressure sensor 211 and the exhaust guidepressure sensor 214 are compared S7 to the desired pressure differenceacross the cylinders 301, 302.

With reference is made to FIG. 7, another embodiment of the method willbe described. Therein steps S1-S3 are identical to the steps S1-S3 inthe embodiment described with reference to FIG. 5. In the embodiment inFIG. 7, in addition to adjusting S4 the exhaust flow restrictionelements 601, 602 in an open loop, the control unit 21 determines S4 bymeans of the data in the data storage unit 213 a setting for the airflow restriction element 903 based on the determined values of theengine torque and the engine rotational speed. The air flow restrictionelement 903 is adjusted S4 in an open loop to the determined setting, soas to provide a restriction of the air flows in the air guide 901correlated with the determined requested engine torque and enginerotational speed.

Further in the embodiment in FIG. 7, based on the determined requestedengine torque and engine rotational speed, the control unit 21determines S5 based on the data in the storage unit 213 a desired airguide pressure value. In a closed loop control, the control unit 21sends signals to the variator 802, based on the desired air guidepressure value and feedback signals from the air guide pressure sensor211, so as to adjust S6 the phase of the camshaft rotation withcorresponding crankshaft angles of the exhaust valve actuation sequencesMOS1, DOS1, COS1. In the closed loop control the feedback signals fromthe air guide pressure sensor 211 are compared S7 to the desired airguide pressure value. Retarding the commencement of the exhaust valveactuation sequences MOS1, DOS1, COS1 will reduce the pressure in the airguide 901, and vice versa.

With reference is made to FIG. 7, an alternative embodiment of themethod will be described. Therein steps are identical to the steps inthe embodiment described with reference to FIG. 7, except for thefollowing differences. Based on the determined requested engine torqueand engine rotational speed, the control unit 21 determines S5 based onthe data in the storage unit 213 a desired pressure difference acrossthe cylinders 301, 302. In a closed loop control, the control unit 21sends signals to the variator 802 so as to adjust S6 the phase of thecamshaft rotation with corresponding crankshaft angles of the exhaustvalve actuation sequences MOS1, DOS1, COS1, based on the desiredpressure difference across the cylinders 301, 302 and feedback signalsfrom the air guide pressure sensor 211 and the exhaust guide pressuresensor 214. In the closed loop control the feedback signals from the airguide pressure sensor 211 and the exhaust guide pressure sensor 214 arecompared S7 to the desired pressure difference across the cylinders 301,302.

It should be noted that in such alternative embodiments, as analternative to the air guide pressure, the camshaft phase adjustment maybe done based on some other suitable feedback parameter, such as therotational speed of the turbocharger 4.

In alternative embodiments of the method, the control unit 21 determinesbased on the determined values of the engine torque and the enginerotational speed and by means of the data in the data storage unit 213,a value of the phase of the camshaft rotation with correspondingcrankshaft angles of the exhaust valve actuation sequences MOS1, DOS1,COS1. The control unit 21 sends signals to the variator 802 so as toadjust the camshaft phase according to the determined phase value. Thecamshaft phase is adjusted with an open loop adjustment based on changesin the requested engine torque and engine rotational speed. In addition,the control unit 21 determines by means of the data in the data storageunit 213 a setting for the air flow restriction element 903 based on thedetermined values of the engine torque and the engine rotational speed.The air flow restriction element 903 is adjusted in an open loop to thedetermined setting, so as to provide a restriction of the air flows inthe air guide 901 correlated with the determined requested engine torqueand engine rotational speed.

Further in such alternative embodiments, based on the determinedrequested engine torque and engine rotational speed, the control unit 21determines based on the data in the storage unit 213 a desired air guidepressure value. Alternatively, a desired pressure difference across thecylinders 301, 302 may be determined as described above. In a closedloop control, the control unit 21 sends signals, based on the desiredair guide value and feedback signals from the air guide pressure sensor211, so as to adjust the first and second exhaust flow restrictionelements 601, 602.

It should be noted that in such alternative embodiments, as analternative to the air guide pressure, the exhaust flow restrictionelement adjustment may be done based on some other suitable parameter,such as the pressure in the exhaust guide 501, 502, or the rotationalspeed of the turbocharger 4.

In other alternative embodiments, at least two of, or all of the exhaustflow restriction element adjustments, the air flow restriction elementadjustments, and the camshaft phase adjustments may be done in a closedloop control. Such closed loop control may be arranged so as for theactual air guide pressure and the actual exhaust guide pressure to equaldesired values of these parameters. The desired air guide pressure andthe desired exhaust guide pressure may be obtained from determinedvalues of the engine speed and the requested engine torque, andcorrelation data stored in the data storage unit. In further alternativeembodiments, the exhaust flow restriction element adjustments, the airflow restriction element adjustments, and/or the camshaft phaseadjustments may be done in a closed loop control so that the actualexhaust guide pressure and the turbocharger speed equal desired valuesof these parameters. The desired exhaust guide pressure and the desiredturbocharger speed may be obtained from determined values of the enginespeed and the requested engine torque, and correlation data stored inthe data storage unit.

Reference is made to FIG. 9. In alternative embodiments of the engine,the turbocharger 4 is a variable geometry turbocharger. whereby theturbocharger 4 provides at the turbine 401 an adjustable flowrestriction function in addition to the flow restriction function of theexhaust flow restriction elements 601, 602. FIG. 9 depicts steps in amethod in such alternative embodiments of the engine.

Similarly to the method described with reference to FIG. 5. when theengine braking is commenced, the supply of fuel to the cylinders 301,302 is terminated S1, and the control valves 809 in the rocker arms 807at the cylinders 301, 302 are controlled to actuate the hydraulicpistons 808 to engage the rocker arms 807 with the decompression noses805 and the charge noses 806 whereby the charging opening sequence COS1and the decompression opening sequence DOS1 are added S2 to the cyclesin the cylinders.

The requested engine torque and the engine rotational speed aredetermined S3. The control unit 21 determines by means of the data inthe data storage unit 213 a setting for the variable geometry turbocharger 4 as well as a setting for the first and second exhaust flowrestriction elements 601, 602 based on the determined values of theengine torque and the engine rotational speed. The variable geometryturbo charger 4 and the exhaust How restriction elements 601, 602 areadjusted S4 to the determined setting, so as to provide a restriction ofthe air flows in the exhaust guides 501, 502 correlated with thedetermined requested engine torque and engine rotational speed. Thisadjustment is an open loop adjustment.

As in FIG. 5, the control unit 21 also determines, based on therequested engine torque and the engine rotational speed, by means of thedata in the data storage unit 213, a setting for the camshaft phase. Inan open loop control, the control unit 21 sends signals to the variator802 so as to adjust S4 the phase of the camshaft rotation to adjust thecrankshaft angles of the exhaust valve actuation sequences MOS1, DOS1,COS1.

Similarly to the method described with reference to FIG. 5, based on thedetermined requested engine torque and engine rotational speed, thecontrol unit 21 determines S5 based on the data in the storage unit 213a desired air guide pressure value. In a closed loop control, thecontrol unit 21 sends signals to the air flow restriction element 903 inthe air guide 901 so as to adjust S6 the air flow restriction element903, based on the desired air guide value and feedback signals from theair guide pressure sensor 211. In the closed loop control, the feedbacksignals from the air guide pressure sensor 211 are compared S7 to thedesired air guide pressure value. As an alternative to the air guidepressure, the air flow restriction element 903 adjustment may be donebased on some other suitable parameter, such as the pressure in theexhaust guide 501, 502, or the rotational speed of the turbocharger 4.

In an engine with a variable geometry turbocharger, alternativeembodiments of the method may include determining based on thedetermined values of the engine torque and the engine rotational speedand by means of the data in the data storage unit 213, settings of thefirst and second exhaust How restriction elements 601, 602 and the airflow restriction element 903, and a value of the phase of the camshaftrotation. The control unit 21 may send signals to the exhaust flowrestriction actuation assembly so as to adjust the exhaust flowrestriction elements 601, 602 according to the determined settings, theair flow restriction element 903 so as to adjust the latter, and to thevariator 802 so as to adjust the camshaft phase according to thedetermined phase value. The exhaust flow restriction elements, the airflow restriction element 903 and the camshaft phase may be adjusted withan open loop adjustment based on changes in the requested engine torqueand engine rotational speed.

Further, in such alternative embodiments, based on the determinedrequested engine torque and engine rotational speed, the control unit 21may determine based on the data in the storage unit 213 a desired airguide pressure value. In a closed loop control, the control unit 21 maysend signals, based on the desired air guide value and feedback signalsfrom the air guide pressure sensor 211, so as to adjust the variablegeometry turbocharger 4. As an alternative to the air guide pressure,the variable geometry turbocharger adjustment may be done based on someother suitable parameter, such as the pressure in the exhaust guide 501,502, or the rotational speed of the turbocharger 4.

In an engine with a variable geometry turbocharger, still furtheralternative embodiments of the method may include determining based onthe determined values of the engine torque and the engine rotationalspeed and by means of the data in the data storage unit 213, a settingof the variable geometry turbocharger 4, a setting of the air flowrestriction element 903, and a value of the phase of the camshaftrotation, and adjusting the variable geometry turbocharger 4 and the airflow restriction element 903 according to the determined settings andadjusting the camshaft phase according to the determined phase value.The variable geometry turbocharger, the air flow restriction element903, and the camshaft phase may be adjusted with an open loop adjustmentbased on changes in the requested engine torque and engine rotationalspeed.

In addition, in such still further alternative embodiments, based on thedetermined requested engine torque and engine rotational speed, thecontrol unit 21 may determine based on the data in the storage unit 213a desired air guide pressure value. In a closed loop control, thecontrol unit 21 may send signals, based on the desired air guide valueand feedback signals from the air guide pressure sensor 211, so as toadjust the exhaust flow restriction elements 601, 602. As an alternativeto the air guide pressure, the exhaust flow restriction elementadjustments may be done based on some other suitable parameter, such asthe pressure in the exhaust guide 501, 502, or the rotational speed ofthe turbocharger 4.

FIG. 10 shows an exhaust flow restriction element 601 for an engineaccording to an additional embodiment of the invention. The exhaust flowrestriction element 601 is a butterfly valve with a flap 604. An exhaustflow restriction actuation assembly 603, comprising a stepper motor, abrushless motor or a pneumatic motor, is provided to adjust the exhaustflow restriction element 601, i.e. to adjust the angular position of theflap 604 around an axle 605. The flap 604 is non-symmetric, i.e. theextension of the flap is larger on one side of the axle 605 than on theother side. As a result, the exhaust flow restriction element isarranged to assume, upon a fault in the exhaust flow restrictionactuation assembly 603, a position in which the exhaust flow restrictionelement does not restrict or block the flow through the exhaust guide.

Reference is made also to FIG. 11 showing a cross-section through acylinder in an engine according to a further embodiment of theinvention. The embodiment in FIG. 11 shares features with the embodimentdescribed above with reference to FIG. 3, except for the followingdistinction: In the embodiment in FIG. 11 there is no adjustable exhaustflow restriction element 601 in the exhaust guide 501.

FIG. 12 depicts steps in a method of controlling the engine in FIG. 11.The method shares features with the method in FIG. 5, expect for thedistinction that the method does not include adjusting any exhaust flowrestriction element. Similarly to the method in FIG. 5, the method inFIG. 12 comprises determining, based on the requested engine torque andthe engine rotational speed, by means of the data in the data storageunit 213, a setting for the camshaft phase, and in an open loop control,adjusting S4 die phase of the camshaft rotation to adjust the crankshaftangles of the exhaust valve actuation sequences MOS1, DOS1, COS1 (FIG.4). In a closed loop control, the air flow restriction clement 903 isadjusted based on the desired air guide pressure value and feedbacksignals from the air guide pressure sensor 211. In the closed loopcontrol, the feedback signals from the air guide pressure sensor 211 arecompared S7 to the desired air guide pressure value. Alternatively, asin FIG. 6. the air flow restriction element 903 maybe adjusted, based ona desired pressure difference across the cylinders 301, 302 and feedbacksignals from the air guide pressure sensor 211 and an exhaust guidepressure sensor.

It is to be understood that the present invention is not limited to theembodiments described above and illustrated in the drawings; rather, theskilled person will recognize that many changes and modifications may bemade within the scope of the appended claims.

1. A method of controlling an internal combustion engine (1) in avehicle comprising a cylinder, a fuel system for supplying fuel to thecylinder, an air guide arranged to guide an air flow to the cylinder, anexhaust guide arranged to guide a gas flow from the cylinder, an exhaustvalve arranged to control a communication between the cylinder, and theexhaust guide, the method comprising controlling the engine to provide abraking torque, the control comprising, terminating the supply of fuelto the cylinder, restricting the flow through the exhaust guide,restricting the flow through the air guide, performing in each of aplurality of cycles of the cylinder an exhaust valve actuation sequence,determining a value of at least one engine parameter affecting thepressure in the cylinder and/or the air mass flow through the cylinder,and in dependence on at least one of the at least one determined engineparameter value adjusting the restriction of the flow through the airguide, wherein the control of the engine to provide a braking torquealso comprises in dependence on at least one of the at least onedetermined engine parameter value adjusting the timing of a commencementof the exhaust valve actuation sequence to occur selectively at anycrankshaft angle within a non-zero crankshaft angle interval.
 2. Amethod according to claim 1, wherein each of the at least one the engineparameter is one of the engine rotational speed, a requested enginebraking torque, a current engine braking torque, a pressure in the airguide, a rotational speed of a turbocharger of the engine, and apressure in the exhaust guide.
 3. A method according to claim 1, whereinadjusting the restriction of the flow through the air guide comprisesadjusting a throttle valve in the air guide.
 4. A method according toclaim 1, wherein the adjustment of the restriction of the flow throughthe air guide is a closed loop adjustment.
 5. A method according toclaim 4, wherein a pressure in the air guide is a feedback parameter inthe closed loop adjustment.
 6. A method according to claim 4, wherein apressure in the exhaust guide is a feedback parameter in the closed loopadjustment.
 7. A method according to claim 1, wherein adjusting thetiming of the commencement of the exhaust valve actuation sequencecomprises adjusting the crankshaft angle at which the exhaust valveactuation sequence is commenced
 8. A method according to claim 1,wherein the adjustment of the timing of the commencement of the exhaustvalve actuation sequence is an open loop adjustment.
 9. A methodaccording to claim 1, wherein the exhaust valve actuation sequencecomprises a decompression opening sequence commenced in a compressionstroke of the cylinder.
 10. A method according to claim 1, wherein theexhaust valve actuation sequence comprises a charging opening sequenceof the exhaust valve commenced in a second half of an intake stroke or afirst half of a compression stroke of the cylinder.
 11. A methodaccording to claim 1, comprising in dependence on at least one of the atleast one determined engine parameter value adjusting the restriction ofthe flow through the exhaust guide.
 12. A method according to claim 11,wherein the adjustment of the restriction of the flow through theexhaust guide is an open loop adjustment.
 13. A method according toclaim 1, wherein restricting the flow through the exhaust guidecomprises adjusting a throttle valve in the exhaust guide, and/oradjusting a flow adjustment function at a turbine of a variable geometryturbocharger of the engine, wherein the exhaust guide is arranged toguide the gas flow from the cylinder to the turbine.
 14. A computercomprising a computer program for causing an internal combustion engineto perform the steps of claim 1 when the program is run on the computer.15. A non-transitory computer readable medium carrying a computerprogram for causing an internal combustion engine to perform the stepsof claim 1 when the program product is run on a computer.
 16. A controlunit configured to perform the steps of the method according to claim 1.17-33. (canceled)